Field of the Disclosure
The present disclosure generally relates to the field of power electronics, and more particularly, to a tuning circuit and a tuning method used in a resonance-type contactless power supply and a resonance-type contactless power supply.
Description of the Related Art
Contactless power supply is widely used in electronic products, especially in low-power electronic products such as cellular phones, MP3 players, digital cameras, laptop computers, and the like, due to their convenience and availability. A conventional contactless power supply usually comprises a transformer consisting of a transmitting coil L1 and a receiving coil L2, and transfers energy from transmitting terminal to receiving terminal by coupling of magnetic field between primary and secondary coils of the transformer.
When electric energy is transferred, inductance values of the transmitting coil and the receiving coil may be changed by various factors such as external obstacles (for example a magnetic conductive object), a load of the power receiver, variations in an operating temperature of the circuit, and variations in locations of the coils. As a result, a resonance frequency of the resonance circuit is changed by variations in the inductance values of the transmitting coil and the receiving coil, and detuning occurs, which decreases significantly a transmission efficiency of the system.
The conventional resonance-type contactless power supply is tuned to a resonance frequency by zero-crossing detection of an inductor current in the transmitting coil. However, such a tuning method needs a zero-crossing detecting circuit with a high precision, because small delay in the zero-crossing detecting circuit will greatly influence the circuit, especially when the resonance frequency is high.